Medical School · Year 3 · Internal Medicine · includes a discussion video

Seminar 19: Rheumatic Diseases

Internal Medicine Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Differentiate inflammatory from non-inflammatory arthritis using clinical features, joint distribution patterns, and laboratory markers
2. Recognize the clinical presentation, diagnostic criteria, and extra-articular manifestations of rheumatoid arthritis and apply treat-to-target principles
3. Describe the multisystem manifestations of systemic lupus erythematosus, interpret autoantibody profiles, and select treatment based on disease severity
4. Apply synovial fluid crystal analysis to diagnose gout and pseudogout and implement appropriate acute and chronic management strategies
5. Identify the shared clinical features of spondyloarthropathies and distinguish ankylosing spondylitis, psoriatic arthritis, and reactive arthritis
6. Formulate a systematic approach to the patient with acute monoarthritis including the recognition and emergency management of septic arthritis

Seminar Outline

Section 1: Approach to Joint Pain

The initial evaluation of joint pain requires distinguishing inflammatory from non-inflammatory etiologies, as this fundamental distinction directs the entire subsequent diagnostic and therapeutic approach. Inflammatory arthritis is characterized by morning stiffness lasting more than one hour, joint swelling with warmth and erythema, worsening of symptoms with prolonged rest, and paradoxical improvement with activity and movement. Non-inflammatory joint conditions, typified by osteoarthritis, produce morning stiffness lasting less than 30 minutes, minimal or absent joint swelling, improvement with rest, and worsening with activity and weight-bearing. Laboratory markers support this distinction: inflammatory arthritis is associated with elevated erythrocyte sedimentation rate and C-reactive protein, reflecting the systemic inflammatory response, while non-inflammatory conditions typically show normal acute phase reactants. This initial categorization narrows the differential diagnosis substantially and prevents the misapplication of immunosuppressive therapies to mechanical joint conditions.

The pattern of joint involvement provides critical diagnostic information that can frequently point toward a specific rheumatologic diagnosis even before laboratory testing is obtained. Monoarticular arthritis, involving a single joint, should always raise concern for septic arthritis and crystal arthropathy, both of which require joint aspiration for definitive diagnosis. Oligoarticular involvement affecting two to four joints is characteristic of reactive arthritis, psoriatic arthritis, and early rheumatoid arthritis. Polyarticular involvement of more than four joints is seen in established rheumatoid arthritis, systemic lupus erythematosus, and viral arthritis. The size of involved joints further refines the differential: small joint involvement at the metacarpophalangeal and proximal interphalangeal joints typifies rheumatoid arthritis, while large joint involvement at the knees, hips, and shoulders is more characteristic of osteoarthritis and spondyloarthropathies. Symmetric involvement suggests rheumatoid arthritis or lupus, whereas asymmetric patterns favor psoriatic arthritis and reactive arthritis.

A thorough clinical history in the evaluation of joint pain must address several key elements that significantly inform the differential diagnosis. The onset of symptoms provides important temporal clues: acute onset over hours suggests crystal arthropathy or septic arthritis, subacute onset over days to weeks suggests reactive or viral arthritis, and insidious onset over weeks to months is typical of rheumatoid arthritis and osteoarthritis. The duration of symptoms distinguishes transient conditions such as viral arthritis, which typically resolves within weeks, from chronic diseases such as rheumatoid arthritis, which persists for months to years. Extra-articular manifestations including skin rashes, gastrointestinal symptoms, ocular inflammation, and oral or genital ulcers point toward specific systemic rheumatic diseases. Family history is particularly relevant for conditions with strong genetic associations, including the HLA-B27-associated spondyloarthropathies and gout.

Red flags in the evaluation of joint pain identify presentations that require urgent diagnostic evaluation and intervention. The combination of fever and acute monoarthritis constitutes a rheumatologic emergency because septic arthritis, if not treated within hours, can cause irreversible joint destruction. Any acute, severe, single joint presentation should be evaluated with joint aspiration to exclude both infection and crystal disease, even when the clinical presentation seems typical for gout. Unexplained weight loss accompanying joint symptoms raises concern for malignancy, which may present with paraneoplastic arthropathy, or for systemic inflammatory conditions such as vasculitis. Specific skin findings provide diagnostic clues: psoriatic plaques suggest psoriatic arthritis, the heliotrope rash and Gottron papules of dermatomyositis indicate inflammatory myopathy, and the malar rash of lupus points toward systemic lupus erythematosus. The presence of any red flag should lower the threshold for specialist referral and expedited diagnostic workup.

<image>Panel A: Comparison chart of inflammatory versus non-inflammatory arthritis showing morning stiffness duration, swelling characteristics, effect of rest and activity, and laboratory markers. Panel B: Joint distribution pattern diagrams showing monoarticular, oligoarticular, and polyarticular involvement with representative diagnoses for each pattern and the distinction between small and large joint disease. Panel C: Timeline of joint symptom onset showing acute, subacute, and insidious presentations with corresponding differential diagnoses and key history elements. Panel D: Red flag identification panel showing fever with monoarthritis, acute severe single joint pain, weight loss, and specific skin findings with the urgent conditions they suggest and required immediate actions.</image>

Section 2: Rheumatoid Arthritis

Rheumatoid arthritis is a chronic systemic autoimmune disease characterized by symmetric inflammatory polyarthritis that preferentially affects the small joints of the hands and feet and, without treatment, leads to progressive joint destruction, deformity, and disability. The classic joint distribution involves the metacarpophalangeal joints, proximal interphalangeal joints, and wrists, with characteristic sparing of the distal interphalangeal joints, a feature that distinguishes rheumatoid arthritis from psoriatic arthritis and osteoarthritis. Morning stiffness exceeding one hour is a hallmark symptom that reflects the intensity of synovial inflammation and improves with activity as the synovial fluid warms and becomes less viscous. Late manifestations of uncontrolled disease include swan neck deformity, in which there is hyperextension of the PIP joint and flexion of the DIP joint; boutonniere deformity, with flexion of the PIP joint and extension of the DIP joint; and ulnar deviation of the fingers at the MCP joints due to weakening and displacement of the extensor tendons.

The 2010 American College of Rheumatology and European League Against Rheumatism classification criteria provide a standardized scoring system for the diagnosis of rheumatoid arthritis. The criteria assign points across four domains: joint involvement, scored from 0 to 5 based on the number and size of affected joints; serology, scored from 0 to 3 based on rheumatoid factor and anti-cyclic citrullinated peptide antibody status; acute phase reactants, scored 0 to 1 based on ESR and CRP elevation; and duration of symptoms, scored 0 to 1 based on whether symptoms have persisted for six weeks or longer. A total score of 6 or greater out of 10 classifies the patient as having definite rheumatoid arthritis. These criteria were designed to facilitate early diagnosis and treatment, recognizing that the window of opportunity for preventing irreversible joint damage is in the first months of disease when aggressive therapy can alter the disease trajectory.

The laboratory evaluation of suspected rheumatoid arthritis includes serologic markers, acute phase reactants, and imaging studies that together support the diagnosis and provide prognostic information. Rheumatoid factor is positive in 70 to 80% of patients with established disease but has limited specificity, as it is also found in other autoimmune conditions, chronic infections, and in up to 15% of healthy elderly individuals. Anti-cyclic citrullinated peptide antibody is more specific for rheumatoid arthritis and, importantly, predicts the development of erosive disease, making it a valuable prognostic marker. Elevation of the erythrocyte sedimentation rate and C-reactive protein reflects the degree of systemic inflammation and is used to monitor disease activity and treatment response. Complete blood count may reveal anemia of chronic disease. Plain radiographs of the hands and feet are the initial imaging modality, showing periarticular osteopenia and joint space narrowing in early disease and marginal erosions in established disease, though MRI and ultrasound can detect synovitis and erosions at earlier stages.

Rheumatoid arthritis is a systemic disease with extra-articular manifestations that affect virtually every organ system and contribute significantly to morbidity and mortality. Pulmonary involvement includes interstitial lung disease, rheumatoid nodules in the lung parenchyma, and pleuritis with pleural effusions characterized by very low glucose and low complement levels. Cardiovascular complications include pericarditis and accelerated coronary artery disease, with RA patients having a cardiovascular mortality risk comparable to diabetes. Rheumatoid nodules are subcutaneous firm nodules found at pressure points, particularly the olecranon and extensor surfaces of the forearms, and are almost exclusively seen in seropositive patients. Ocular manifestations include scleritis, a painful inflammatory condition that can lead to scleral thinning and perforation if untreated, and episcleritis, which is less severe. Felty syndrome, the triad of rheumatoid arthritis, splenomegaly, and neutropenia, is a rare but serious complication associated with recurrent infections and requires aggressive treatment of the underlying RA.

<image>Panel A: Hand and joint diagrams showing the classic distribution of rheumatoid arthritis affecting MCP, PIP, and wrist joints with DIP sparing and illustrations of swan neck, boutonniere, and ulnar deviation deformities. Panel B: 2010 ACR/EULAR classification criteria scoring system showing the four domains of joint involvement, serology, acute phase reactants, and symptom duration with point assignments and the diagnostic threshold of 6 points. Panel C: Laboratory evaluation panel showing RF sensitivity and specificity, anti-CCP prognostic value, ESR/CRP as disease activity markers, and radiographic progression from periarticular osteopenia to erosions. Panel D: Extra-articular manifestations diagram showing pulmonary involvement with ILD and nodules, cardiovascular disease with pericarditis and accelerated CAD, rheumatoid nodules, ocular scleritis, and Felty syndrome.</image>

Section 3: RA Treatment

The treatment philosophy for rheumatoid arthritis has evolved to embrace a treat-to-target strategy in which therapy is escalated until a predefined disease activity target is achieved, analogous to treat-to-target approaches in diabetes and hypertension. The primary target is clinical remission, defined by validated composite measures such as the DAS28 score below 2.6 or the ACR/EULAR Boolean remission criteria requiring tender joint count, swollen joint count, CRP, and patient global assessment all at or below 1. When remission is not achievable, low disease activity represents an acceptable alternative target. Disease activity is reassessed at regular intervals, typically every 3 months, and therapy is adjusted until the target is reached. This approach has been shown to produce superior outcomes compared to conventional care, including higher remission rates, less radiographic progression, better functional outcomes, and improved quality of life.

Disease-modifying antirheumatic drugs are the cornerstone of RA treatment because they alter the underlying disease course rather than simply providing symptomatic relief. Methotrexate is the first-line DMARD for most patients, administered as a weekly dose typically starting at 15 mg and titrated up to 25 mg weekly, with folic acid supplementation to reduce side effects. Methotrexate works by inhibiting dihydrofolate reductase and has anti-inflammatory properties that reduce joint inflammation and prevent erosive damage. Hydroxychloroquine is used for mild disease and as part of combination therapy, requiring periodic ophthalmologic monitoring for retinal toxicity, which is rare but can be irreversible. Sulfasalazine may be combined with methotrexate in triple therapy regimens. Leflunomide, a pyrimidine synthesis inhibitor, serves as an alternative first-line agent for patients who cannot tolerate methotrexate. All conventional DMARDs require monitoring for hepatotoxicity, cytopenias, and other organ-specific adverse effects.

Biologic DMARDs represent a major therapeutic advancement for patients with inadequate response to conventional DMARDs and target specific molecules within the inflammatory cascade. Tumor necrosis factor inhibitors, including etanercept, adalimumab, and infliximab, were the first biologics developed for RA and remain the most widely used class, with proven efficacy in reducing inflammation, preventing erosions, and improving functional outcomes. Interleukin-6 receptor inhibitors, exemplified by tocilizumab, suppress the systemic inflammatory response and may be used as monotherapy when methotrexate is contraindicated. Rituximab depletes B cells through targeting the CD20 surface antigen and is typically reserved for patients who have failed TNF inhibitors. Abatacept modulates T-cell costimulation by blocking the CD80/CD86-CD28 interaction. Janus kinase inhibitors, including tofacitinib and baricitinib, are oral targeted synthetic DMARDs that inhibit intracellular signaling downstream of multiple cytokine receptors, offering the convenience of oral administration with efficacy comparable to biologic agents.

The treatment algorithm for rheumatoid arthritis follows a stepwise escalation approach beginning with conventional DMARDs and progressing to biologic agents based on treatment response and disease severity. First-line therapy for all newly diagnosed RA patients is methotrexate, often combined with a short course of low-dose glucocorticoids to provide rapid symptom relief while waiting for the DMARD to take effect, which typically requires 4 to 8 weeks. If the treatment target is not achieved after an adequate trial of methotrexate at optimal doses, the next step is to add or switch to a biologic DMARD, with the choice of agent guided by comorbidities, patient preference, and practical considerations such as route of administration. Patients who are anti-CCP positive are more likely to develop erosive disease and may benefit from more aggressive initial therapy. NSAIDs serve only as adjunctive symptom control and should never be used as monotherapy because they do not prevent joint destruction. Glucocorticoids should be used at the lowest effective dose for the shortest duration to minimize long-term adverse effects including osteoporosis, diabetes, and cardiovascular disease.

<image>Panel A: Treat-to-target strategy diagram showing disease activity assessment at 3-month intervals, target of remission or low disease activity, therapy adjustment steps, and validated composite measures including DAS28. Panel B: Conventional DMARD overview showing methotrexate as first-line with dosing, hydroxychloroquine for mild disease, sulfasalazine and leflunomide as alternatives with monitoring requirements for each agent. Panel C: Biologic DMARD mechanism chart showing TNF inhibitors, IL-6 inhibitors, B-cell depletion, T-cell costimulation blockade, and JAK inhibitors with their molecular targets and representative agents. Panel D: Stepwise treatment algorithm from methotrexate monotherapy through inadequate response to biologic addition with the role of glucocorticoids, NSAIDs, and prognostic factors guiding therapy intensity.</image>

Section 4: Systemic Lupus Erythematosus

Systemic lupus erythematosus is a chronic multisystem autoimmune disease characterized by the production of autoantibodies against nuclear components, immune complex deposition, and inflammation affecting virtually any organ system. The disease demonstrates a striking predilection for women of childbearing age, with a female-to-male ratio of approximately 9:1, and disproportionately affects individuals of African American, Hispanic, and Asian descent. Cutaneous manifestations include the classic malar or butterfly rash, a photosensitive erythematous eruption over the cheeks and nasal bridge that spares the nasolabial folds; discoid lupus, which produces scarring, depigmented plaques; and diffuse photosensitivity with skin reactions to ultraviolet light exposure. Joint involvement occurs in over 90% of patients and typically manifests as a non-erosive, non-deforming symmetric polyarthritis, distinguishing it from rheumatoid arthritis. Renal involvement in the form of lupus nephritis is one of the most serious manifestations and occurs in approximately 50% of patients, potentially progressing to end-stage renal disease. Additional organ involvement includes hematologic abnormalities including cytopenias and hemolytic anemia, neuropsychiatric manifestations including seizures and psychosis, and serositis with pleuritis and pericarditis.

The diagnosis of systemic lupus erythematosus relies on the integration of clinical findings and immunologic markers through classification criteria. The SLICC criteria require at least four criteria, including at least one clinical and one immunologic criterion, or alternatively, biopsy-proven lupus nephritis in the presence of ANA or anti-dsDNA antibodies. Key clinical criteria include the malar rash, oral ulcers, arthritis, serositis, renal involvement, neurologic involvement, and hematologic abnormalities. The immunologic criteria encompass ANA, anti-dsDNA, anti-Smith, antiphospholipid antibodies, low complement levels, and direct Coombs test positivity. The more recent 2019 EULAR/ACR criteria use a weighted scoring system with ANA positivity as an entry criterion, assigning points for clinical and immunologic domains, with a score of 10 or higher classifying the patient as having SLE. Regardless of the classification system used, clinical judgment remains paramount, as no single criterion is pathognomonic for lupus.

The autoantibody profile in SLE provides critical information for diagnosis, prognosis, and monitoring of disease activity. Antinuclear antibody is the most sensitive serologic test, present in over 99% of SLE patients, but it is not specific, as it can be found in many other autoimmune conditions and in healthy individuals. Anti-double-stranded DNA antibody is highly specific for SLE and its levels correlate with lupus nephritis activity, making it useful for both diagnosis and disease monitoring. Anti-Smith antibody is the most specific autoantibody for SLE but is present in only 20 to 30% of patients. Anti-SSA and anti-SSB antibodies are associated with neonatal lupus, photosensitivity, and overlap with Sjogren syndrome. Antiphospholipid antibodies, including anticardiolipin, anti-beta2-glycoprotein I, and lupus anticoagulant, are found in approximately one-third of SLE patients and confer increased risk of thrombosis and pregnancy complications.

Complement levels serve as important biomarkers of disease activity in SLE because the complement system is directly consumed during the process of immune complex formation and clearance. Serum C3 and C4 levels are characteristically low during active disease, reflecting complement consumption by immune complexes deposited in tissues. The total hemolytic complement (CH50) is also reduced during active flares. Monitoring complement levels in conjunction with anti-dsDNA titers provides a dual-marker approach to disease activity assessment: rising anti-dsDNA and falling complement levels often herald an impending disease flare, enabling preemptive treatment intensification. Conversely, normalizing complement levels and declining anti-dsDNA titers suggest disease quiescence and may support tapering of immunosuppressive therapy. This biomarker-guided approach to management has become a cornerstone of modern SLE care.

<image>Panel A: Clinical manifestations of SLE organized by organ system showing malar rash, discoid lesions, and photosensitivity for skin; non-erosive arthritis for joints; lupus nephritis for kidneys; cytopenias for hematologic; seizures and psychosis for neuropsychiatric; and pleuritis and pericarditis for serositis. Panel B: SLICC classification criteria showing the requirement for 4 criteria with at least 1 clinical and 1 immunologic, or biopsy-proven lupus nephritis with key criteria listed. Panel C: Autoantibody profile showing ANA sensitivity, anti-dsDNA specificity and nephritis correlation, anti-Smith high specificity, anti-SSA/SSB associations, and antiphospholipid antibody thrombosis risk. Panel D: Complement monitoring diagram showing C3, C4, and CH50 levels during active disease and remission with anti-dsDNA correlation and the dual-marker approach to predicting flares.</image>

Section 5: SLE Management

The management of SLE is guided by the principle that all patients should receive hydroxychloroquine as a foundational therapy, regardless of disease severity, based on strong evidence that it reduces flares, prevents organ damage accumulation, improves survival, and has a favorable safety profile. Hydroxychloroquine at a dose not exceeding 5 mg/kg/day reduces the risk of lupus flares by approximately 50% and has been shown to lower the risk of renal involvement and thrombotic events. Sun protection is essential for all SLE patients because ultraviolet light exposure is a known trigger for disease flares, and patients should be counseled on the use of broad-spectrum sunscreen, protective clothing, and avoidance of peak sun exposure. Cardiovascular risk management is increasingly recognized as critical because SLE patients have markedly accelerated atherosclerosis with cardiovascular event rates 5 to 10 times higher than age-matched controls. Pregnancy planning requires careful timing during disease quiescence and screening for antiphospholipid antibodies and anti-SSA antibodies that may affect maternal and fetal outcomes.

The treatment of SLE is stratified by disease severity, with mild disease managed conservatively and severe organ-threatening disease requiring aggressive immunosuppression. Mild manifestations including skin rashes, arthritis, and mild serositis are managed with hydroxychloroquine and NSAIDs, with short courses of low-dose prednisone added for acute flares. Moderate disease with more prominent constitutional symptoms or moderate organ involvement may require low-dose prednisone on a sustained basis along with a steroid-sparing immunosuppressive agent. Severe disease, particularly lupus nephritis and central nervous system involvement, necessitates high-dose glucocorticoids typically initiated as intravenous pulse methylprednisolone followed by oral prednisone, combined with potent immunosuppressive induction therapy. Lupus nephritis, classified histologically by ISN/RPS class, is treated with either mycophenolate mofetil or cyclophosphamide as induction therapy, followed by mycophenolate or azathioprine as maintenance therapy to prevent relapse.

The immunosuppressive armamentarium for SLE includes several agents with distinct mechanisms and toxicity profiles that are selected based on the specific organ manifestation and disease severity. Azathioprine is a purine analog used as maintenance therapy and as a steroid-sparing agent for non-renal manifestations. Mycophenolate mofetil inhibits de novo purine synthesis in lymphocytes and is the preferred agent for both induction and maintenance of lupus nephritis, with efficacy comparable to cyclophosphamide for induction and superior tolerability. Cyclophosphamide is an alkylating agent reserved for severe organ-threatening disease, particularly proliferative lupus nephritis and CNS lupus, due to its potent immunosuppressive effect and its significant toxicities including gonadal failure, hemorrhagic cystitis, and increased malignancy risk. Belimumab, a monoclonal antibody targeting the B-lymphocyte stimulator, is the first biologic approved specifically for SLE and is used as add-on therapy for patients with active disease despite standard treatment. Rituximab, while not formally approved for SLE, is used off-label for refractory cases, particularly refractory nephritis and severe cytopenias.

Monitoring of SLE requires regular assessment of disease activity, organ function, and treatment toxicity. Urinalysis should be performed at every clinical visit because the onset of lupus nephritis may be clinically silent, detectable only by the appearance of proteinuria, hematuria, or cellular casts. Serum creatinine and estimated glomerular filtration rate are monitored regularly to detect renal function decline. Complement levels and anti-dsDNA titers are tracked as markers of disease activity, with changes often preceding clinical flares by weeks. Patients on hydroxychloroquine require annual ophthalmologic examination after 5 years of use, or earlier in patients with renal impairment, to screen for retinal toxicity, which is dose- and duration-dependent. Complete blood count monitoring is essential for detecting drug-induced cytopenias from immunosuppressive agents and for identifying lupus-related hematologic abnormalities. Bone density screening and cardiovascular risk assessment should be performed regularly given the long-term effects of glucocorticoid therapy and the inherent cardiovascular risk of SLE.

<image>Panel A: Foundational SLE management showing hydroxychloroquine for all patients with its benefits of flare reduction, organ damage prevention, and survival improvement alongside sun protection and cardiovascular risk management. Panel B: Severity-based treatment ladder showing mild disease with HCQ and NSAIDs, moderate disease with low-dose prednisone and steroid-sparing agents, and severe disease with pulse steroids and mycophenolate or cyclophosphamide for nephritis. Panel C: Immunosuppressive agent comparison showing azathioprine, mycophenolate, cyclophosphamide, belimumab, and rituximab with their mechanisms, indications, and key toxicities. Panel D: Monitoring schedule showing urinalysis at every visit, creatinine monitoring, complement and anti-dsDNA tracking, ophthalmologic screening on hydroxychloroquine, and bone density assessment with monitoring intervals.</image>

Section 6: Crystal Arthropathies

Gout is the most common inflammatory arthritis, caused by the deposition of monosodium urate crystals in joints and surrounding tissues in the setting of chronic hyperuricemia. The first metatarsophalangeal joint is the most frequently affected site, a presentation termed podagra, though the ankle, knee, midfoot, wrist, and elbow are also commonly involved. Acute gouty arthritis presents as sudden-onset, severe, monoarticular joint pain with dramatic erythema, warmth, and swelling that typically reaches peak intensity within 12 to 24 hours. Risk factors for gout include male sex, obesity, alcohol consumption particularly beer and spirits, dietary purine excess from red meat and shellfish, thiazide and loop diuretics, chronic kidney disease, and organ transplant recipients on cyclosporine. Definitive diagnosis requires joint aspiration with demonstration of needle-shaped, negatively birefringent crystals under polarized light microscopy, which appear yellow when aligned parallel to the compensator and blue when perpendicular. While hyperuricemia is a necessary precondition for gout, serum uric acid levels may be normal during an acute attack due to the uricosuric effect of inflammation, and a normal uric acid level does not exclude the diagnosis.

The acute management of gouty arthritis focuses on rapid suppression of the intense inflammatory response triggered by crystal deposition. Nonsteroidal anti-inflammatory drugs such as indomethacin and naproxen at full anti-inflammatory doses are first-line therapy when not contraindicated. Colchicine is most effective when initiated within 36 hours of symptom onset, with a low-dose regimen of 1.2 mg followed by 0.6 mg one hour later demonstrated in the AGREE trial to be as effective as high-dose colchicine with significantly fewer gastrointestinal side effects. Glucocorticoids, administered orally, intramuscularly, or by intra-articular injection, are the preferred option when NSAIDs and colchicine are contraindicated, such as in patients with renal insufficiency, heart failure, or concomitant anticoagulation. Ice application provides adjunctive symptomatic relief. Critically, urate-lowering therapy should not be initiated during an acute flare because rapid fluctuations in serum uric acid levels can paradoxically prolong or worsen the attack by destabilizing existing crystal deposits.

Chronic gout management centers on urate-lowering therapy to reduce serum uric acid below 6 mg/dL, which is below the saturation threshold for monosodium urate crystallization and allows dissolution of existing crystal deposits over time. Allopurinol, a xanthine oxidase inhibitor, is the first-line urate-lowering agent, initiated at a low dose of 100 mg daily and gradually titrated upward based on serum uric acid levels, with dose adjustments required in renal impairment. Febuxostat is an alternative xanthine oxidase inhibitor for patients intolerant of allopurinol, though the CARES trial raised concerns about cardiovascular mortality that have led to its positioning as a second-line agent. Probenecid, a uricosuric agent that enhances renal uric acid excretion, is an option for patients with adequate renal function who are under-excretors of uric acid. Pegloticase, a recombinant uricase that enzymatically converts uric acid to the more soluble allantoin, is reserved for severe refractory tophaceous gout. When initiating urate-lowering therapy, prophylactic colchicine at 0.6 mg once or twice daily should be co-administered for 3 to 6 months to prevent the mobilization flares that commonly occur as serum uric acid levels decline and crystal deposits begin to dissolve.

Calcium pyrophosphate deposition disease, commonly known as pseudogout, is a crystal arthropathy caused by the deposition of calcium pyrophosphate dihydrate crystals in articular cartilage and synovial fluid. The knee and wrist are the most commonly affected joints, distinguishing pseudogout from gout, which preferentially affects the first MTP joint. Radiographic chondrocalcinosis, the calcification of articular cartilage visible on plain films, is a characteristic finding seen in the knee menisci, triangular fibrocartilage of the wrist, and the symphysis pubis, though its presence does not necessarily indicate symptomatic disease. Definitive diagnosis requires joint aspiration with identification of rhomboid-shaped, positively birefringent crystals under polarized light microscopy, appearing blue when parallel to the compensator and yellow when perpendicular, which is the opposite pattern of urate crystals. Acute pseudogout is managed with NSAIDs, colchicine, or glucocorticoids, similar to gout. Unlike gout, there is no effective urate-lowering equivalent for CPPD disease, and treatment focuses on symptom management and identification of associated metabolic conditions including hyperparathyroidism, hemochromatosis, and hypomagnesemia.

<image>Panel A: Gout clinical presentation showing podagra at the first MTP joint, risk factors, crystal morphology with needle-shaped negatively birefringent appearance under polarized light, and the importance of joint aspiration for definitive diagnosis. Panel B: Acute gout treatment algorithm showing NSAIDs, low-dose colchicine, and glucocorticoids as first-line options with contraindications and the prohibition against starting ULT during acute flares. Panel C: Chronic gout management showing urate-lowering therapy target below 6 mg/dL with allopurinol as first-line, febuxostat, probenecid, and pegloticase with prophylactic colchicine during ULT initiation. Panel D: CPPD disease comparison with gout showing rhomboid positively birefringent crystals, knee and wrist predilection, chondrocalcinosis on radiograph, and associated metabolic conditions requiring screening.</image>

Section 7: Spondyloarthropathies

The spondyloarthropathies are a family of chronic inflammatory arthritides that share several unifying clinical features distinguishing them from rheumatoid arthritis and other autoimmune conditions. Inflammatory back pain, the cardinal symptom, is characterized by onset before age 40, insidious development, improvement with exercise and worsening with rest, and morning stiffness exceeding 30 minutes that does not improve with immobility, which is the opposite pattern of mechanical low back pain. The HLA-B27 allele is associated with the spondyloarthropathies, particularly ankylosing spondylitis, in which it is present in approximately 90% of Caucasian patients, though the presence of HLA-B27 is neither necessary nor sufficient for diagnosis. Axial involvement with sacroiliitis and spinal inflammation is the defining feature, but peripheral manifestations are common and include enthesitis, the inflammation at tendon and ligament insertion sites, and dactylitis, a diffuse swelling of an entire digit known as a sausage digit that results from inflammation of the joint, tendon sheath, and surrounding soft tissues simultaneously. Extra-articular manifestations include anterior uveitis, inflammatory bowel disease, and psoriasis, reflecting the overlap between these related conditions.

Ankylosing spondylitis is the prototypical spondyloarthropathy, characterized by progressive inflammatory involvement of the sacroiliac joints and spine leading to eventual ankylosis if untreated. The disease typically presents in young adults under age 45 with chronic low back pain lasting more than 3 months that improves with exercise, and physical examination may reveal reduced spinal mobility and the Schober test demonstrates limited lumbar flexion. Imaging is essential for diagnosis: plain radiographs may show sacroiliitis with sclerosis, erosions, and eventual fusion of the sacroiliac joints, along with vertebral squaring, syndesmophytes, and the classic bamboo spine appearance of advanced disease. MRI is more sensitive for early disease, detecting bone marrow edema at the sacroiliac joints before structural changes are visible on plain films. Complications include anterior uveitis in approximately 30% of patients, aortitis with aortic regurgitation, and restrictive lung disease from chest wall rigidity. Treatment begins with regular exercise and NSAIDs as first-line pharmacologic therapy, followed by TNF inhibitors and IL-17 inhibitors for patients with inadequate response.

Psoriatic arthritis is an inflammatory arthritis associated with psoriasis that presents with distinctive clinical patterns and characteristic imaging findings. The most common pattern is asymmetric oligoarthritis, though psoriatic arthritis may also present as symmetric polyarthritis mimicking rheumatoid arthritis, distal interphalangeal joint predominant disease, arthritis mutilans with severe osteolysis, and spondyloarthritis with axial involvement. Nail changes including pitting, onycholysis, and subungual hyperkeratosis are present in the majority of patients with psoriatic arthritis and may precede or accompany the articular manifestations. Skin psoriasis typically precedes the onset of arthritis by years, though in approximately 15% of cases the arthritis appears first. Radiographic findings include the distinctive pencil-in-cup deformity resulting from osteolysis of the proximal phalanx with widening of the distal phalanx, periostitis with new bone formation along the shafts of affected phalanges, and joint ankylosis in advanced disease. Treatment options include methotrexate for peripheral disease, and TNF inhibitors, IL-17 inhibitors, and IL-23 inhibitors for more severe or refractory disease.

Reactive arthritis is a sterile inflammatory arthritis that develops following a genitourinary or gastrointestinal infection, typically manifesting 1 to 4 weeks after the inciting infection. The classic triad, formerly known as Reiter syndrome, consists of arthritis, urethritis, and conjunctivitis, though the complete triad is present in only a minority of patients. Common triggering infections include Chlamydia trachomatis for genitourinary infections and Salmonella, Shigella, Campylobacter, and Yersinia for enteric infections. The arthritis is characteristically asymmetric and predominantly affects the large joints of the lower extremities, particularly the knee and ankle. The clinical course is typically self-limited, with the majority of patients experiencing resolution within 3 to 12 months, though approximately 15 to 20% of patients develop chronic arthritis. Treatment during the acute phase centers on NSAIDs for symptom control, with intra-articular glucocorticoid injections for persistent monoarthritis. Antibiotics are indicated for active genitourinary Chlamydia infection but do not alter the course of the arthritis once it has developed. DMARDs including sulfasalazine and methotrexate are reserved for patients with chronic or refractory disease.

<image>Panel A: Shared features of spondyloarthropathies showing inflammatory back pain characteristics, HLA-B27 association, axial involvement with sacroiliitis, enthesitis at tendon insertion sites, dactylitis with sausage digit appearance, and extra-articular manifestations. Panel B: Ankylosing spondylitis progression from early sacroiliitis on MRI through radiographic sacroiliitis to bamboo spine with syndesmophytes, along with complications of uveitis, aortitis, and restrictive lung disease. Panel C: Psoriatic arthritis patterns showing asymmetric oligoarthritis, DIP predominant, polyarthritis, arthritis mutilans, and spondyloarthritis with nail changes and pencil-in-cup deformity on radiograph. Panel D: Reactive arthritis showing triggering infections, classic triad of arthritis, urethritis, and conjunctivitis, asymmetric lower extremity pattern, and timeline from infection to arthritis onset with treatment options.</image>

Section 8: Other Connective Tissue Diseases

Sjogren syndrome is a chronic autoimmune condition characterized by lymphocytic infiltration and destruction of exocrine glands, primarily the salivary and lacrimal glands, producing the hallmark symptoms of xerostomia (dry mouth) and xerophthalmia (dry eyes) known as the sicca syndrome. Primary Sjogren syndrome occurs in isolation, while secondary Sjogren syndrome develops in the context of another autoimmune disease such as rheumatoid arthritis or systemic lupus erythematosus. The disease predominantly affects middle-aged women, with a female-to-male ratio exceeding 9:1. Diagnosis is supported by the presence of anti-SSA (Ro) and anti-SSB (La) antibodies, Schirmer test demonstrating reduced tear production, and labial salivary gland biopsy showing focal lymphocytic sialadenitis with a focus score of 1 or greater. Extraglandular manifestations include interstitial lung disease, renal tubular acidosis, peripheral neuropathy, and importantly, a significantly increased risk of non-Hodgkin lymphoma, estimated at 5 to 10% over the disease course, necessitating surveillance for lymphoproliferative disease. Treatment is primarily symptomatic with artificial tears, saliva substitutes, and muscarinic agonists such as pilocarpine and cevimeline to stimulate residual glandular function.

Systemic sclerosis, also known as scleroderma, is a connective tissue disease characterized by progressive fibrosis of the skin and internal organs, vasculopathy, and immune activation. The disease is classified into two major subtypes based on the extent of skin involvement. Limited cutaneous systemic sclerosis, formerly described by the CREST acronym, involves skin thickening restricted to the face and distal extremities and is associated with calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia. The anti-centromere antibody is characteristic of limited disease and is associated with a lower risk of interstitial lung disease but a higher risk of pulmonary arterial hypertension developing after years of disease. Diffuse cutaneous systemic sclerosis involves rapid and widespread skin thickening extending proximal to the elbows and knees, with earlier and more severe internal organ involvement. The anti-Scl-70 (anti-topoisomerase I) antibody is associated with diffuse disease and carries a high risk of pulmonary fibrosis. Major complications include scleroderma renal crisis, characterized by acute hypertension, microangiopathic hemolytic anemia, and rapidly progressive renal failure, which is treated with ACE inhibitors.

The inflammatory myopathies encompass a group of autoimmune conditions characterized by proximal skeletal muscle weakness and elevated muscle enzymes, with dermatomyositis and polymyositis being the principal subtypes. Dermatomyositis presents with characteristic cutaneous manifestations alongside proximal muscle weakness: the heliotrope rash is a violaceous discoloration of the eyelids, and Gottron papules are erythematous papules over the dorsal aspects of the MCP, PIP, and DIP joints and extensor surfaces of the elbows and knees. Polymyositis presents with symmetric proximal muscle weakness without the distinctive skin findings. Laboratory evaluation reveals markedly elevated creatine kinase, which serves as a marker of disease activity, along with aldolase and myoglobin elevation. Anti-Jo-1 antibody identifies the antisynthetase syndrome, characterized by interstitial lung disease, mechanic's hands, arthritis, and Raynaud phenomenon. Both dermatomyositis and polymyositis carry an increased risk of occult malignancy, particularly ovarian, lung, breast, and gastrointestinal cancers, necessitating age-appropriate cancer screening at diagnosis. Treatment involves high-dose glucocorticoids as initial therapy, with steroid-sparing immunosuppressive agents including methotrexate, azathioprine, and mycophenolate mofetil.

Vasculitis represents a diverse group of conditions characterized by inflammation and destruction of blood vessel walls, classified primarily by the size of the predominantly affected vessels. Large vessel vasculitis includes giant cell arteritis, which affects the temporal and other cranial arteries in patients over 50 and can cause blindness from ophthalmic artery involvement, and Takayasu arteritis, which affects the aorta and its major branches in young women. Medium vessel vasculitis includes polyarteritis nodosa, which spares the pulmonary vasculature and is associated with hepatitis B, and Kawasaki disease, which causes coronary artery aneurysms in children. Small vessel vasculitis includes the ANCA-associated vasculitides: granulomatosis with polyangiitis (GPA, formerly Wegener) associated with c-ANCA/PR3, microscopic polyangiitis (MPA) associated with p-ANCA/MPO, and eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss). IgA vasculitis, formerly Henoch-Schonlein purpura, presents with palpable purpura, arthritis, abdominal pain, and renal involvement predominantly in children. The diagnostic approach to vasculitis focuses on identifying the pattern of organ involvement and the size of the affected vessels to narrow the differential diagnosis and guide targeted laboratory testing and biopsy.

<image>Panel A: Sjogren syndrome showing lymphocytic infiltration of salivary and lacrimal glands with sicca symptoms, anti-SSA/SSB antibodies, Schirmer test, salivary gland biopsy, lymphoma risk, and symptomatic treatment options. Panel B: Systemic sclerosis classification showing limited versus diffuse cutaneous disease with associated antibodies (anti-centromere and anti-Scl-70), CREST features, and major complications including pulmonary fibrosis, PAH, and renal crisis. Panel C: Inflammatory myopathies showing dermatomyositis heliotrope rash and Gottron papules, polymyositis proximal weakness, elevated CK, anti-Jo-1 and antisynthetase syndrome, malignancy association, and treatment with steroids. Panel D: Vasculitis classification by vessel size showing large (GCA, Takayasu), medium (PAN, Kawasaki), and small (GPA, MPA, EGPA, IgA vasculitis) vessel diseases with ANCA associations and organ involvement patterns.</image>

Section 9: Septic Arthritis

Septic arthritis is a medical emergency requiring immediate recognition and treatment because untreated infection can destroy articular cartilage within hours to days, leading to permanent joint damage and potentially life-threatening systemic sepsis. The presentation is characteristically acute, with monoarticular involvement in over 80% of cases, and the knee is the most commonly affected joint, followed by the hip, shoulder, ankle, and wrist. Patients typically present with an acutely swollen, erythematous, warm, and exquisitely painful joint with significant limitation of range of motion, accompanied by systemic signs of infection including fever and malaise. Risk factors for non-gonococcal septic arthritis include pre-existing joint disease such as rheumatoid arthritis or osteoarthritis, prosthetic joints, recent joint surgery or injection, immunocompromised states including diabetes and HIV, and intravenous drug use. Staphylococcus aureus is the most common causative organism in non-gonococcal septic arthritis, accounting for approximately 50 to 70% of cases in adults.

The diagnosis of septic arthritis rests on synovial fluid analysis obtained by arthrocentesis, which must be performed urgently in any patient with suspected joint infection. Synovial fluid in septic arthritis typically demonstrates a white blood cell count exceeding 50,000 per cubic millimeter with greater than 90% polymorphonuclear leukocyte predominance, though lower counts do not exclude infection, particularly in immunocompromised patients. Gram stain of the synovial fluid is positive in only 50 to 75% of non-gonococcal cases but when positive provides immediate guidance for empiric antibiotic selection. Synovial fluid culture is the definitive diagnostic test, though it may take 24 to 48 hours to return positive, and blood cultures should be obtained simultaneously because bacteremia is present in approximately 50% of cases. Crystal analysis should always be performed concurrently because gout and septic arthritis can coexist, and the presence of crystals alone does not exclude concomitant infection. Imaging with plain radiographs may show joint space widening from effusion and soft tissue swelling but is normal early in the disease course.

Treatment of septic arthritis requires prompt initiation of empiric intravenous antibiotics and adequate joint drainage, both of which are essential for preserving joint function and preventing sepsis. Empiric antibiotic therapy is initiated immediately after synovial fluid and blood cultures are obtained, with the choice of agent guided by the patient's age, risk factors, and Gram stain results. Vancomycin provides coverage for methicillin-resistant Staphylococcus aureus and is commonly included in empiric regimens, combined with a third-generation cephalosporin such as ceftriaxone to cover gram-negative organisms. Once culture and sensitivity results are available, antibiotics are narrowed to the most targeted effective agent. The duration of antibiotic therapy is typically 2 to 4 weeks for most organisms, with longer courses of 4 to 6 weeks recommended for Staphylococcus aureus. Joint drainage is performed by serial aspiration, which may need to be repeated daily until effusion resolves, or by surgical drainage with arthroscopic or open lavage when the hip joint is involved, when serial aspiration is technically difficult or ineffective, or when there is evidence of joint destruction.

Gonococcal arthritis must be distinguished from non-gonococcal septic arthritis because of its different epidemiology, clinical presentation, and prognosis. Disseminated gonococcal infection typically affects young, sexually active adults and presents in two overlapping phases. The bacteremic phase manifests as a migratory polyarthralgia with vesiculopustular skin lesions, tenosynovitis, and constitutional symptoms, while the localized phase involves a septic monoarthritis typically affecting the knee, wrist, or ankle. The diagnosis can be challenging because synovial fluid cultures are positive in only 20 to 50% of gonococcal arthritis cases, and nucleic acid amplification testing of the synovial fluid and genitourinary specimens improves diagnostic yield. The prognosis of gonococcal arthritis is significantly better than non-gonococcal septic arthritis, with low rates of permanent joint damage when treated promptly. Treatment consists of ceftriaxone 1 gram intravenously or intramuscularly daily combined with azithromycin 1 gram orally as a single dose to cover potential concurrent chlamydial infection, with transition to oral therapy guided by sensitivity results after clinical improvement, for a total treatment duration of at least 7 days.

<image>Panel A: Septic arthritis emergency presentation showing acute monoarticular swelling with erythema, most commonly at the knee, risk factors including prior joint disease, immunosuppression, and IV drug use, and Staphylococcus aureus as the predominant organism. Panel B: Synovial fluid analysis in septic arthritis showing WBC above 50,000 with PMN predominance, Gram stain sensitivity of 50-75%, culture as definitive test, and the importance of concurrent crystal analysis to exclude coexisting gout. Panel C: Treatment protocol showing empiric vancomycin plus ceftriaxone, culture-directed narrowing, 2-4 week duration with longer for S. aureus, and joint drainage by serial aspiration or surgical lavage with indications for each approach. Panel D: Gonococcal versus non-gonococcal arthritis comparison showing different demographics, migratory polyarthralgia and skin lesions in gonococcal disease, lower synovial fluid culture yield, better prognosis, and ceftriaxone plus azithromycin treatment regimen.</image>

Section 10: Approach to Positive ANA

The interpretation of a positive antinuclear antibody test requires careful integration of the clinical context because ANA positivity is common in the general population and does not, by itself, diagnose any specific disease. Approximately 15% of healthy individuals have a positive ANA at low titers, and the prevalence increases with age. The titer of the ANA carries diagnostic significance: a titer of 1:40 is considered low and is frequently found in healthy individuals, a titer of 1:160 is moderate and warrants further investigation when accompanied by compatible clinical symptoms, and a titer of 1:640 or greater is high and is more likely to be clinically significant. The ANA should not be ordered as a screening test in asymptomatic patients because the high false-positive rate leads to unnecessary anxiety, additional testing, and inappropriate specialist referrals. The most appropriate use of ANA testing is in patients with clinical features suggestive of a systemic autoimmune condition, where the result can contribute meaningful diagnostic information.

When an ANA is positive in a symptomatic patient, further serologic testing is directed by the clinical presentation and aims to identify the specific autoantibody profile associated with the suspected diagnosis. Anti-dsDNA antibody is ordered when lupus is suspected, as it is highly specific for SLE and correlates with nephritis activity. Anti-Smith antibody is the most specific autoantibody for SLE but is present in only a minority of patients. Anti-SSA (Ro) and anti-SSB (La) antibodies are associated with Sjogren syndrome and are important to identify in women of childbearing age because anti-SSA antibodies cross the placenta and can cause neonatal lupus including congenital heart block. Anti-ribonucleoprotein (RNP) antibody in high titers is the hallmark of mixed connective tissue disease, which features overlapping clinical features of SLE, scleroderma, and polymyositis. Clinical correlation is essential at every step because no autoantibody is pathognomonic in isolation, and the diagnosis of a systemic autoimmune disease should never rest on a single laboratory test.

A positive ANA is found across a wide spectrum of autoimmune conditions with varying frequency, reflecting the shared underlying mechanism of loss of self-tolerance to nuclear antigens. SLE has the highest ANA prevalence at greater than 99%, meaning that a negative ANA effectively rules out lupus. Drug-induced lupus also produces a positive ANA in virtually all cases, with anti-histone antibodies serving as the characteristic marker. Sjogren syndrome and systemic sclerosis are ANA-positive in approximately 85% of cases. Inflammatory myopathies show ANA positivity in 40 to 80% of cases. Rheumatoid arthritis has a 30% ANA positivity rate, which can create diagnostic confusion when joint symptoms are the predominant feature. The key principle is that the clinical presentation must guide the interpretation: a positive ANA in a patient with sicca symptoms points toward Sjogren syndrome, while the same result in a patient with proximal muscle weakness directs the evaluation toward inflammatory myopathy.

Several clinical pearls guide the appropriate use and interpretation of ANA testing in practice. The most important principle is to avoid ordering ANA in the absence of clinical features suggestive of an autoimmune condition, as the high false-positive rate makes screening of asymptomatic individuals counterproductive. A negative ANA has the greatest clinical utility because it effectively rules out SLE with a negative predictive value approaching 100%, and it is very unlikely in Sjogren syndrome and systemic sclerosis. Higher ANA titers are more likely to be associated with clinically significant autoimmune disease, though even high-titer ANAs can be found incidentally in healthy individuals. The ANA pattern on immunofluorescence, which describes the distribution of nuclear staining as homogeneous, speckled, nucleolar, or centromere, was historically used to predict specific antibody types but has limited diagnostic utility with current specific antibody testing. The cornerstone of managing a positive ANA is a thorough clinical evaluation and selective confirmatory antibody testing, avoiding the reflexive ordering of extensive autoimmune panels that generate more confusion than clarity.

<image>Panel A: ANA titer interpretation showing 1:40 as low with common false positives, 1:160 as moderate warranting investigation if symptomatic, and 1:640 or greater as high with likely clinical significance, alongside the 15% healthy population ANA positivity rate. Panel B: Directed serologic workup following positive ANA showing anti-dsDNA for lupus, anti-Smith for SLE specificity, anti-SSA/SSB for Sjogren, anti-RNP for mixed CTD, and the principle of clinical correlation at each step. Panel C: ANA prevalence across autoimmune conditions showing greater than 99% in SLE and drug-induced lupus, 85% in Sjogren and scleroderma, 40-80% in myositis, and 30% in RA with diagnostic implications. Panel D: Clinical pearls for ANA testing showing the rule against screening asymptomatic patients, the value of a negative ANA in ruling out SLE, titer significance, limited utility of ANA pattern, and the principle of selective confirmatory testing.</image>

Summary

• Inflammatory arthritis: morning stiffness exceeding one hour, joint swelling with warmth, elevated ESR/CRP; non-inflammatory: brief stiffness, worsening with activity
• RA: symmetric small joint polyarthritis with RF and anti-CCP positivity; treat-to-target with methotrexate as first-line DMARD
• SLE: multisystem disease with malar rash, nephritis, and cytopenias; anti-dsDNA correlates with nephritis; low complement indicates active disease
• All SLE patients receive hydroxychloroquine; lupus nephritis requires mycophenolate or cyclophosphamide induction
• Gout: needle-shaped, negatively birefringent crystals; acute treatment with NSAIDs, colchicine, or steroids; do not start ULT during flare
• Chronic gout: allopurinol first-line targeting serum uric acid below 6 mg/dL with prophylactic colchicine during ULT initiation
• Spondyloarthropathies: inflammatory back pain, HLA-B27 association, enthesitis, and dactylitis; TNF and IL-17 inhibitors for refractory disease
• Ankylosing spondylitis: young adults with chronic back pain, sacroiliitis on MRI, and bamboo spine; NSAIDs first-line
• Septic arthritis: emergency requiring immediate aspiration and IV antibiotics; S. aureus most common; WBC above 50,000 with PMN predominance
• Positive ANA: correlate with clinical symptoms; negative ANA effectively rules out SLE; avoid screening asymptomatic patients

Key Terms

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